The present invention relates to a heat resisting alloyed steel and, more particularly, to a heat resisting alloyed steel capable of exhibiting a high compressive strength at elevated temperature.
The present invention pertains to the heat resisting alloyed steel which is suited as a material for rails or like guides installed on the hearth within a heating furnace and which can exhibit a high compressive strength at the elevated temperature within the range of from 1,250.degree. to 1,300.degree. C.
An alloyed steel, which contains, in addition to iron, 30% chromium and 50% cobalt as essential components thereof, is well known as having a high resistance to elevated temperature, for example, 1,250.degree. to 1,300.degree. C. Because of this physical property, this 30%C- 50%Co-Fe alloyed steel has heretofore largely used as a material for rails or like guides installed on the hearth within a heating furnace. The rails prepared from this known alloyed steel have exhibited a practically acceptable durability even though subjected to the elevated temperature within the range of 1,250.degree. to 1,300.degree. C., but is not considered satisfactory for the following reason.
With reference to FIG. 1 of the accompanying drawings, an equilibrium diagram of alloyed steels containing iron, chromium and cobalt is shown as having isothermal lines exhibited at the temperature of 600.degree. C. The composition of the alloyed steel containing 30% chromium, 50% cobalt and 20% iron is indicated by a point marked by a. As can be seen from the equilibrium diagram, the known alloyed steel used as a material for the rails represents a structure having a .alpha.-Co phase and .sigma.-phase. Because of instability in structure due to precipitation of the .sigma.-phase, the known alloyed steel is susceptible to cracking when a load is imposed thereon.